Ernst Alexanderson
electromagnetism
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Alexanderson alternator
- Before 1904, many inventors, including Nikola Tesla,
- created an alternator to generate an electromagnetic frequency,
- but none of these produced a frequency high enough
- for radio transmission; they were all under twenty kilohertz.
- However, in 1904, Reginald Fessenden, working for
- National Electric Signaling Company, contracted with GE
- for an alternator to produce up to a hundred kilohertz
- for continuous wave radio transmission.
- Ernst Alexanderson designed an alternator whose frequency
- was controlled by a rotor with hundreds of narrow slots
- that caused a variable reluctance to interrupt the flux,
- which induced a radio-frequency voltage in a set of coils.
Transoceanic broadcasts
- The Alexanderson alternator allowed the installation
- of broadcast stations around the world for broadcasting transoceanic
- high-power longwave radiotelegraphic messages in Morse code,
- which became an urgent requirement during World War I.
Alexanderson Day
- The Varberg Radio Station
- near Grimeton, Sweden,
- celebrates Alexanderson Day
- by broadcasting Morse
- code messages on 17.2 kHz
- using the last working
- Alexanderson alternator.
The box
- People thought
- you needed
- a spark-gap transmitter
- to make radio waves.
- Today we call that
- thinking inside the box.
In 1903, Charles Proteus Steinmetz of GE delivered a ten-kilohertz alternator-transmitter, which Fessenden could not use as a radio transmitter. Ernst Alexanderson’s effort was far more successful; however, alternator-transmitters were eventually replaced by vacuum-tube transmitters.
See also in The book of science:
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